Electric furnace



Aug-D M) Y. R. @GRNELHUg ELECTRIC FURNACE Filed Jan. 16, 1935 6Sheets-Sheet l ATTORNEY.

m 1%? Y. R. GQRNELHUS y ELECTRIC FURNACE Filed Jan. 16, 1935 6Sheets-Sheet 2 INVENTOR ELECTRIC FURNACE Filed Jan. 16, 1955 6SheetS-Sheei 3 ATTORNEY.

Aug, 1 1937 Y. R. CORNELHUS 5 ELECTRIC FURNACE F"Z5. I F ZZ W9,

7 {y I Qa 222% Q 9 5 Z 5% j U Z6 25 26 5 1 6 1 GO INVENTOR -1 ,1937. Y.R. CORNELIUS 2,089,690

ELECTRIC FURNACE Filed Jan. 16, 1935 6 Shets-Sheet 5 F"..7]. a 48 7 W Aai 35W;

INVENTOR Mar F4. Coin .42 /05,

BY J

ATTORNEY.

9 1937. Y. R. CORNELIUS 2,089,690

ELECTRIC FURNACE Filed Jan. 16, 1935 6 Sheets-Sheet 6 ATTORNEY.

Patented Aug. 10, 1937 V UNITED STATES PATENT OFFICE Application January16, 1935, Serial No. 2,003 In Canada December 24, 1934 16 Claims.

The present invention relates to the construction and operation ofelectric furnaces of the single or polyphase type such as may be usedfor the manufacture of glass, sodium silicate or other products.

The principal object of the invention is to construct and operate afurnace of the above type so as to maintain the charge or other materialin the fusion zone at a uniform temperature without localizedoverheating or the formation therein of overheated zones.

Another object of the invention is the arrangement of electrodes withinsuch a furnace so that they will influence the flow of material from thereaction or melting zone.

Other objects will appear as the description proceeds and with referenceto the accompanying drawings, showing several embodiments of theinvention.

When constructing electric furnaces for the manufacture of glass, sodiumsilicate and similar products, it is of the utmost importance that thetemperature of the molten bath in the furnace chamber be as uniform aspossible. This is necessary in order to avoid convection currents in thebath, which latter may cause serious damage to the furnace lining anddisturbance and hindrance of the chemical reactions taking place in thebath. Convection currents further tend to cause portions of the unmeltedor unreacted charge to pass through the furnace outlet, thuscontaminating the final product. This desirable equalized temperature isparticularly difficult to obtain in the operation of three or polyphasefurnaces while in single phase operations a fairly r uniform bathtemperature may be maintained by.

using heavy iron electrodes which have the effect of transferring theheat from the warmer places to the cooler ones.

In three or polyphase furnaces, however, such heavy electrodes cannot beused as the cubical content of the electrodes can vary only within arelatively narrow range, which is controlled by the melting area, theelectrode gap and operating voltage. The use of. such heavy electrodeswould require a much larger melting area or fusing zone in the furnaceand lower operating voltage than has been considered good practice inthree phase furnace operation.

It has been further found to be of advantage to increase the operatingvoltage over that considered suitable heretofore. Instead of the usualaverage of 60 to '70 volts, satisfactory results have been obtainedbetween a voltage range of 120 to 130. This, of course, permits of theuse of smaller electrodes and less electrode contact su face. Onedisadvantage, however, of the use of this smaller contact area is thatthe electrical load per square unit of electrode contact surface reachesa dangerous maximum.

When operating single phase furnaces, it has been considered that themaximum electrical load should not at any time exceed to 6 amperes persquare inch of electrode area. This precaution has been taken to avoidelectrode overheating which might otherwise possibly cause a melting ofthe electrode and consequent decomposition or contamination of thematerial of the bath itself. In order to make three phase furnaceoperation commercially acceptable, it has been necessary to double theelectrical load to from 10 to 12 amperes per square inch of electrodearea, so that the volume of the electrodes and the area of their contactsurfaces will correspond with the optimum furnace melting area andoperating voltage. It has, therefore, become necessary to use electrodesless in volume and area, in many instances such reduction being of thatused in single phase furnaces. The electrodes in three or polyphasefurnaces, therefore, lack the desirable protection obtainable in singlephase furnace electrodes by reason of their larger volume. Consequentlythey tend to overheat with the formation of local overheated zones andundesirable convection currents.

While heat is generated more or less in all parts of the meltingchamber, yet the bulk thereof will be generated around the center partof each electrode gap. Consequently, in three phase furnaces containingthree electrodes, three distinct heat zones will appear. This is to beexpected inasmuch as the current density is greatest at these points.Unfortunately, such heat zones tend to increase in intensity and size asthe electrical conductivity increases with the heat and more currentpasses therethrough until an equilibrium is reached between the heatgenerated at those locations and the heat removed therefrom either byconduction or radiation.

The material flowing from the melting chamber or fusing zone through thesubmerged throat into the tapping or refining chamber tends to have asuction effect on the melt surrounding the throat in the meltingchamber. This causes the melt closest to the throat to move fasterdownwardly toward the throat than in other parts of the melt.Consequently, more raw material moves in this bath and will be fused atthis point. The fusing process, which requires heat, results in coolingthe molten mass, which, in turn, causes increased electrical resistanceand less heat to be generated, thus further intensifying the coolingeffect.

The above mentioned causes tend to work in combination with each otherand in actual operations temperature differences of 100 C. and more indifferent parts of the furnace have been observed. This is serious inglass furnaces where it causes bubbles or seeds in the product.

It has also been found that, in order to enhance and maintain theuniformity of the temperature of the molten charge, it is advisable toapply heat to certain parts of the furnace bottom not to an extent whichwould actually raise the temperature of the molten charge but rather tocompensate for heat radiation or conduction.

Great care must be taken in designing the location of the furnace wallsso that no substantial part of the current flow passes through suchwalls. If this precaution is ignored, serious deterioration of the wallsdue to .ls current flow has been actually found to have taken place infurnaces which have been torn down for repair or replacement.Calculations for such design to avoid this effect are more fullydescribed in my copending patent application, Serial No. 719,076.

Sometimes it is impractical to locate the furnace walls entirely outsideof this current path. In such event, the furnace walls should be placedas far away from this current path as possible, this path generallybeing theoretically not materially outside a semi-circle drawn from thecenter point of one electrode to the center point of an oppositeelectrode. If this semi-circle touches or tends to touch a wall, meansshould be provided for cooling this particular part of the wall. Thismay be done by providing cooling ducts in the wall at that place or bysubstituting for insulation there, a material which will readily disspate developed heat such as cast refractory or the like.

The raw material fed to the furnace may be used as a means to decreaseor increase the electrical conductivity of the resistance of the moltenbath itself and this feature is also described in my copendingapplication above mentioned. In any event, the raw material blanketcovering the surface of the melt should have such a minimum thicknessthat gases penetrating the same leave the blanket at substantially thetemperature of the fresh raw material. It must, however. be thick enoughthat there will be no gas pockets between the bottom. of the blanket andthe surface of the melt. This raw material may be evenly spread over thefurnace by a motor driven charging car capable of being raised orlowered, all as described in my above mentioned copending application.

To this end, the invention contemplates, with respect both to single andpolyphase furnaces, means for applying heat to the bottom of the melt,both in and outside of the reaction or melting chamber to compensate forheat losses through radiation or conduction.

The invention also contemplates the provision of cooling means to avoidwall deterioration for those portions of the side walls through whichthe current flow passes or tends to flow.

The invention further revolves about the use of electrodes having anupstanding plate-like extension, the volume of which has a certainproportion to the volume of that portion of the electrode submerged orin contact with the melt; also about having the connector bars of theelectrodes located or extending out of or above the melt.

The invention contemplates with particular respect to polyphasefurnaces, an arrangement of electrodes whereby locally overheated zonesare avoided and a uniform melt temperature may be maintained. Wherethere is a tendency for heat 70 loss to occur at or near the submergedthroat or outlet from the melting or reaction zone, the

invention contemplates the arrangement of electrodes so that this heatloss may be avoided and the discharge from the furnace melting chamber75 will proceed with uniformity without in any of course, between theway detracting from the desirable temperature uniformity of the entiremelt.

The invention further consists in the novel arrangement and constructionand combination of parts and operating details more fully hereinafterdescribed and shown in the accompanying drawings.

In the drawings:

Fig. 1 is a diagrammatic plan view of a polyphase furnace showingcertain undesirable heat zones;

Fig. 2 is a similar veiw of a furnace showing how the deficiencies ofFig. 1 may be corrected;

Fig. 3 is a diagrammatic plan view of a modifled form of polyphasefurnace;

Fig. 4 is a diagrammatic plan view of still another form of polyphasefurnace;

Fig, 5 is a plan view through a preferred form of furnace;

Fig. 6 is a diagrammatic furnace hook-up;

Fig. 7 is a diagrammatic plan view showing a modified form of electrodearrangement:

Fig. 8 is a diagrammatic plan view showing a modified form of electrodearrangement;

Fig. 9 is a diagrammatic plan view showing a modified form of electrodearrangement;

Fig. 10 is a diagrammatic plan view showing a modified form of electrodearrangement;

Fig. 11 is a plan View of a complete furnace constructed according tothis invention;

Fig. 12 is a sectional elevation along the line l2=l2 of Fig. 11;

Fig. 13 is a sectional elevation along the line i3--l3 of Fig. 11;

Fig. 14 is an elevation partly in section along the line i l-44 in Fig.11;

Fig. 15 is a side view of one form of electrode;

Fig. 16 is an end view of the electrode of Fig. 15;

F1Figisl'l is a bottom plan view of the electrode of Fig. 18 is a sideview of a modified form of electrode;

Fig. 19 is an end view of the electrode of Fig. 18; v

Fig. 20 is a bottom plan view of Fig. 18.

Referring now with particularity to the drawings, the difficultiesusually encountered in a three electrode polyphase furnace areillustrated in Fig. 1. Such a furnace is diagrammatically illustratedashaving walls or wall-sections I forming with a bottom-section amelting or reaction chamber 2 therebetween with a submerged throat 3, arefining chamber 4 and overflow 5. Electrodes 8, I and 8 which aresubstantially horizontally disposed and are suitably connected to apolyphase electric circuit are also provided. The normal location ofthese electrodes is one in which a horizontal triangle connecting thecam ters of the electrodes comprises a triangle whose angles are so thatthey are directed toward a generally common center, electrode 1 being ona longitudinal center line of the furnace and in line with the submergedthroat 3, the remaining electrodes being on each side thereof. Underthese circumstances, a most unsatisfactory heat distribution occurs. 1

Due to the fact that the flow of the melt through the submerged throat 3tends to be faster than that of the melt in the remaining portion of theheat chamber, there is relative stagnation in those parts of the furnaceaway from the throat. The zones of greatest heat intensity are,electrodes in the stagnant plan view showing a zone. This, therefore,produces localized superheated spots as indicated by the lines 9 and Illbetween electrodes 6 and I and 'l and 8, respectively. The entirestagnant zone is indicated by the line H. This makes, of course, zonesof varying degrees of heat, in which zones 9 and I!) are the hottest,zone I l is slightly cooler, while the remaining portion of the furnacechamber is still cooler. The coolest zone, which is over i the furnacethroat, iscaused by the more rapid outflow of fused material through thethroat causing additional quantities of the raw charge to be drawn down,and the fusion of the larger quantities of raw charge at this pointabsorbs heat to produce a cooling action on the charge at this point. Inaddition, in the warmer zone ll,

convection currents will tend to be set up which,

in combination with the down current in the colder' zone immediatelyadjacent the throat, causes an increase of the temperature differential.The above makes for unsatisfactory operation which is directly reflectedin the quality of the product.

Fig. 2 illustrates a furnace of the type shown in Fig. 1 but in whichthe heat balance has been vastly improved, Here the furnace layout isshown similar in some respects to that of the furnace of Fig. 1, exceptthat immediately within the walls l a platform i2 is built up on thefurnace bottom and electrodes l3, l4 and |rest on this platform. Theplatform i2 is not completely circular but is provided with spaced apartends immediately adjacent the submerged throat 3. This produces astepped melting or reaction chamber indicated generally at l6.

As will be observed, the gap between electrodes l3 and 15 has beenshortened as compared with the gaps between electrodes l3 and M and I4and l 5. This tends to increase the heat generated be-- 40 tweenelectrodes l3 and I5. This increased heat tends to overcome the coolingeffect of the indrawn raw material produced as a result of the suctioneffect of the melt passing through the submerged throat 3. It alsoresults in a merging 45 of all three heat zones between the electrodesinto a single zone illustrated diagrammatically by the line H.

While, of course, it is difficult to set down formulae whereby the exactlocation of these 5" electrodes may be determined for all purposes, yetit has been determined that in a horizontal triangle connecting thecenters of the electrodes, the angles made with the line connecting thetwo electrodes on each side of the submerged throat 5.1 should be morethan 60, while the top angle of the triangle will be less than 60. Morespecifically the electrode gaps a: and y should be approximately the 2times the electrode gap e.

In order to further enhance the uniform heat- 50 ing effect in such afurnace and to prevent undue deterioration of the furnace walls, it isdesirable, as has been noted in my copending application Serial No.719,076, that the walls of the furnace should be so spaced as to be outof the path of current flow. This flow may be representeddiagrammatically by the semi-circles F connecting the center points ofthe electrodes. The deteriorating effect of the heat generated by thecurrent flow where such flow tends to touch the T0 Walls may be greatlylessened by placing a cooling duct l8 between the inside refractory l9and the outer metallic shell 28, or any desirable cooling means whichwill remove the heat from this section of the furnace wall. Castrefractory 2| 75 may be used to serve the same function as the coolingduct, this material being particularly efficacious in conducting heataway from the melting zone at that point. This material is alsoparticularly resistant to the current flow itself, but rather thanconstruct the entire inner lining of this material, which would berather expensive, blocks thereof may be inserted at the points ofgreatest wear.

Cooling ducts 22 may also be provided in the platform l2 to overcome anylocal overheating. It is to be noted that these ducts pass immediatelybeneath the electrodes and serve to maintain those parts of the furnaceadjacent thereto at a' desirable temperature.

Fig. 3 illustrates a polyphase furnace having four electrodes in whichthe walls are indicated generally at I, the melting chamber or reactionzone at 2, the submerged throat 3 leading to the refining chamber 4 andoverflow 5.. A platform (2 is built up on the furnace bottom to receivethe electrodes 23, 24, 25 and 26. Electrodes 23 and 25 may be of largervolume and extent than electrodes 24 and 26 where desirable. In thisarrangement, electrodes 23 and 25 are in line with the furnace centerline A-A while electrodes 24 and 26 are in line with the furnace centerline B-B. Electrodes 23 and 25 are each connected with a different phasein a three phase electrical circuit while electrodes 24 and'26 areconnected to the same and remaining phase.

It is to be noted that the submerged throat 3 is in line with the gapbetween electrodes 23 and 25 and also passes beneath the former. Thismakes for a. better heat control. By adjusting the contact areas ofelectrodes 23 and 25 with relation to electrodes 24 and 28, theuniformity of heating effect may likewise be controlled.

An arrangement as described above tends to produce local heat zones ofgreatest intensity as illustrated by the lines 21, with a lesser heatzone indicated by the line 28, the remaining portion of the furnaceimmediately surrounding the throat 3 being cooler. In a furnace of thisgeneral layout, however, these zones are not excessively objectionable,although the heat uniformity can be improved by the arrangement shown inFig. 4.

In that layout, the furnace dimension along the center line B--B ismaterially shortened over that of Fig. 3. This brings the electrodes 24and 26 closer together with the result that the gaps be.- tween thoseelectrodes and electrodes 23 and 25 are materially shortened. This has atendency to bring the zones 2'1 closer together and the limits of zone23 closer to the throat 3 which, as a consequence, materially decreasesthe cold zone immodiately surrounding the throat. This enlargement ofthe hot zone in the center of the furnace is very desirable.

While it is difiicult to arrive at formulae for a most desirablelocation of the electrodes with regard to each other, yet it maygenerally be stated that the angle between the lines connecting thecenters of electrodes connected to different phases should beapproximately 90. This may be expressed by saying that the length of thegapbetween the electrodes on the furnace center line AA should be /2times that of the average of the shorter gaps.

The same relationship of furnace wall to current flow should be observedwith respect to that described in connection with Fig. 2 as well as thevarious cooling means or ducts there provided.

To further equalize the temperature attained in the heat zones of afurnace of the type shown in Fig. 4, an electrode arrangement as shownin Fig. 5 is preferred. By moving the electrodes 24 and 26 out of thefurnace center line BB and into the line parallel therewith but nearerthe submerged throat 3, practically all localized heat 5 zones aremerged into a single zone of fairly uniform intensity. The top of thiszone is illustrated by the line 29 and the bottom thereof by the line33. The relationship in Fig. 5 as to electrode gap should be the same asabove set forth 1 in connection with Fig. 4. This adjustment is sosensitive that even a small movement of the electrodes out of thefurnace center line B-B' results in appreciable heat uniformity.

In Fig. 6, a three phase furnace is diagrammatically illustrated showingthe walls I and the electrodes 23, 24, 25 and 26 in which electrode 23is connected to phase A, electrode 25 with phase B, electrodes 24 and 26with phase C. In this arrangement, the effective area of electrodes 23and 25 and their volume is materially greater than that of electrodes 24and 26.

This larger effective area and volume may be secured in other ways thanby making an integrally larger electrode.

In Fig. 7, the same furnace is shown in which the electrode 23 issubdivided into two individual electrodes both, however, connected withphase A as in the case of Fig. 6.

In Fig. 8, both electrodes 23 and are of the s 30 multiple typeconnected, however, in the manner shown in Fig. 6.

In like manner, either or both of the electrodes 24 and 26 may besubdivided as shown in Figs. 9 and 10, respectively, wherein electrodes24 and/or 2B are of the multiple variety. The above illustrates the widediversification that may be practiced to secure the herein desirableeffects.

A complete furnace embodying the principles herein described is shown inFigs. 11 to 14 inelusive.

In Fig. 11 the furnace shell is shown at 31 enclosing a composite wallmade up of insulation material 32 with refractory lining 33. The majorportion of the bottom of the furnace chamber between the side walls iscomposed of refractory 33 mounted upon suitable insulation 32 restedupon supporting blocks 34. A portion of this refractory 33 surrounds thebottom immediately adjacent to said walls to form the platform i2 uponwhich the electrodes rest. Cooling ducts 35 are located in various partsof the furnace construction in order to produce the desired coolingeifect where needed.

In order to compensate for any heat lost by radiation or conduction fromthe molten material when passing through the submerged throat 3, thebottom of the furnace immediately beneath and on each side of thesubmerged throat 3 is made of a more efilcient heat conductor such asfused refractory 36. Immediately below are located a series of metallicblocks 31 such as iron or the like through which passes heating meanssuch as carbon resistance 33 connected at the ends by carbon leads 39 toa suitable source of electric current. By generating heat at this point,any heat lost throughradiation or conduction is resupplied. This makesfor a uniformity of heating effect and, as a matter of fact, byincreasing 70 the heat at this point, the fluidity of the batch may beincreased here. In like manner, heat may be supplied to the bottom ofthe refining chamber 4 or elsewhere as desired.

In order to induce bow through the submerged 75 throat I, the bottom ofthe melting chamber is inclined toward the center to form a trough 40,leading to the throat I.

In operation, the raw material is fed to the melting or reaction chamberby means of a charging car 4i suitably mounted for movement on rails 42on the top of the furnace wall, this car being also mounted for verticaladjustment so as to maintain a desired thickness or blanket of rawmaterial 43 on top of the melt. The level of the molten material in thefurnace should preferably be such that the major portions of theelectrodes are submerged therein while the connector bars of theelectrodes are not. The upper portion of the electrode, however, whichextends toward and outside of the furnace walls, desirably should becompletely surrounded by the raw material blanket.

The melt flows through the submerged throat to the refining chamber 4,the level of which is maintained at the level of the discharge outlet 5under the pressure action of the raw material blanket 43.

Where desirable, the walls of the refining chamber or zone may beprovided with apertures 44 through which a flame from any desired sourcesuch as a gas burning flame may be projected to maintain the surface ofthe material therein at the desired temperature for eliminating the undesirable bubbles, grains or seed and thereby making the meltsubstantially homogeneous. Thus, heating means are provided for both topand bottom sections of the melt in the refining zone. For retaining thiszone against excessive heat losses it is also desirable to provide acover 45 for the refining chamber.

It is also to be noted that cooling ducts II or their equivalent areprovided in the furnace walls to prevent wall deterioration where thecurrent flow between electrodes touches or tends to touch such walls.

Desirable types of electrodes are shown in Figs. 15 to 20, inclusive.

In Figs. 15 to 17 inclusive, such electrodes have a substantiallycylindrical portion 46 provided with an upstanding connection plate 41having a portion 48 for connection outside the furnace to the electricalbus bars. The connection for each electrode between the submergedportion and the furnace wall is above the molten material. The advantageof this is that if this connecting bar were in the melt, then currentwould flow from the submerged bar portion through the melt adjacent thefurnace wall with resulting excessive heating in zones adjacent the walland consequent undue wear in the furnace wall.

In Figs. 18 to20 inclusive, the electrodes are shown as having amodified contact contour as at 49. In order to maintain the desired heatbalance and to prevent overheating of that portion of the electrode incontact with the material to be treated, the connecting plate of theelectrodes should have a volume not less than that of the parts 46 and49.

Obviously, the specifictypes of electrodes above described as well asthe heating means for the furnace bottom or other parts where heatcompensation is needed, may be used in any of the various forms offurnaces above described.

While the furnaces have been descrbed with reference to particularembodiments, yet it is to be understood that the invention is not to berestricted thereto but is to be construed broadly and limited only bythe scope of the claims.

I claim:

1. A polyphase electric furnace comprising a chamber for the material tobe melted and in which the material acts as a resistance, spacedhorizontally disposed electrodes therein directed toward a generallycommon center, two of said electrodes being opposite each other, each ofwhich is connected to a different phase in a three phase electricalsystem, and two additional electrodes opposite each other and on a lineat right angles to a line connecting the first two electrodes, the twolatter electrodes being connected to the third. phase in the said threephase electrical system.

2. A polyphase electric furnace comprising a $5 chamber for the materialto be melted and in which the material acts as a resistance, spacedhorizontally disposed electrodes therein directed toward a generallycommon center, two of said electrodes being opposite each other along acenter line of the furnace, each of which is con.- nected with adifferent phase in a three phase electrical system, and two additionalelectrodes one on each side of the former and along a center linetransverse to the first mentioned center line, both of said electrodesbeing connected to the third phase in the said three phase electricalsystem.

3. The furnace of claim 1 in which at least one of said electrodes issubdivided into several electrodes.

4. The furnace of claim 2 in which the distance of the gap between theelectrodes on a furnace center line is greater than the gap betweeneither electrode on the transverse center line and either of the centerline electrodes.

5. The furnace of claim 2 in which the distance of the gap between theelectrodes on the center line is #5 times the gap between eitherelectrode on the transverse center line and either of the 40 center lineelectrodes.

6. A polyphase electric furnace for the material to be melted and inwhich the material acts as a resistance, comprising a chamber, twoelectrodes therein opposite each other along the center line 46 of thefurnace, each of which is connected with a different phase in a threephase electrical system, and two additional electrodes on each side ofthe former, both of which are connected to the third phase in the saidthree phase system, the furnace s so having a submerged outlet throatthrough one of the side walls crossed by the center line, the twoadditional electrodes being located between the transverse center lineand the side wall of the furnace through which the submerged outletpasses and all of said electrode entering the melt.

5 bottom and side walls forming an operating chamber therebetween,platforms set on the furnace floorand in proximity to the furnace walls,electrodes resting on said platforms, said electrodes being positionedwith respect to the side 70 walls so that said side walls are outside ofthe path of the current passing between all of said electrodes, twoelectrodes at opposite side walls I along the center line of the furnaceeach connected with a different phase of a three phase electrical systemand two additional electrodes at opposite side walls along a linetransverse with the center line both of which are connected to the thirdphase in said three-phase system, said furnace having a submerged outletalong the center line of the furnace passing beneath the platform and aside wall into an adjoining chamber.

9. The furnace of claim 8 with heat accumulating blocks of a materialdifferent from that of which the furnace bottom is made, and means toheat said blocks.

10. The furnace of claim 8, in which the bottom of said chamber consistsof refractory material, metal blocks of large volume beneath the sameand heating means for said blocks within the same.

11. The furnace of claim 8 provided with a refining chamber and asubmerged throat connecting the two chambers, heat accumulating blocksbeneath the floor of the throat and the refining chamber and heatingmeans associated with said blocks.

12. An electric furnace comprising side walls and a bottom forming atreating chamber there- 'between, platforms placed on the furnace bottomand in proximity to the side walls, electrodes resting on saidplatforms, said electrodes having a plate-shaped connection rising fromthe top thereof and extending horizontally out beyond the side wall to asuitable electrical connection, the plate-shaped connection beingadapted to be covered by a raw material blanket formed on the top of themolten mass within the furnace by the raw material fed thereto, themajor portion of the electrode being adapted to be submerged in themolten mass.

13. The furnace of claim 12 in which the connection plate of theelectrode represents at least one third of the weight of the electrodepart adapted to be below the surface of the molten mass.

14. A polyphase electric furnace comprising a chamber, a submergedthroat for the discharge of material treated therein, an electrode oneach side of said throat, a third electrode on the other side of saidchamber and in line with said throat, the gap between the two electrodeson each side of the throat being so much less than that between saidelectrodes and the third electrode, that the temperature throughout ahorizontal section of the fusing zone will be practically equal.

15. A polyphase electric furnace comprising a chamber, a submergedthroat for the discharge of material treated therein, an electrode oneach side of said throat, a third electrode on the other side of saidchamber and in line with said throat, the gap between the two electrodeson each side of the throat being so much less than that between saidelectrodes and the third electrode, that the temperature throughout ahorizontal section of the fusing zone will be practically equal, themolten charge in the chamber being covered by a thick raw materialblanket which is continuously fed to the furnace.

16. An electric furnace comprising furnace walls and a furnace bottomdefining a space adapted for containing a conductive bath formed from asuperposed layer of raw material to be treated in the furnace, aplurality of electrodes between which current is adapted to flow throughthe conductive bath, and electrical connections for said electrodesentering the raw material layer for being cooled thereby.

YNGVE R. CORNELIUS.

